Glutamic acid decarboxylase activity of the olfactory bulb in male rats is influenced by olfactory stimuli and hormonal status

Changes in glutamate decarboxylase activity (GAD) in the main (MOB) and accessory (AOB) olfactory bulbs were determined at 11:00 hr and 17:00 hr in intact odor deprived (IOD) male rats exposed to female olfactory stimuli, and in castrated odor deprived males (COD) either injected with testosterone (T), exposed to female pheromone or injected with T and exposed to pheromone. Grouping IOD males by female olfactory stimulus and time of the day, MOB and AOB-GAD activity changed in the morning and not in the afternoon. In COD males, T injection induced an increased response in MOB-GAD activity 24 hr later either in the morning or in the afternoon, while no changes were seen at 11.00 or 17.00 hr by exposure to female odor. In the AOB of COD males, both T administration or exposure to female pheromone, only induced an increase of enzyme activity in the morning. The association of T and female pheromone, decreased morning GAD activity both in the MOB and in the AOB compared with the values of COD males treated with T. In the afternoon this association had no effect compared with the MOB, AOB-GAD activity of COD males injected with testosterone. These results indicate that hormonal and olfactory inputs in IOD and COD males are effective in changing olfactory bulb-GAD activity mainly in the morning.